Thanks Tom that makes sense. (In this case I'm fairly sure that the FTS 1050 is at least meeting it's 100 sec ADEV spec of 1E-12 I have had results in the 13's on occasion when looking at other oscilators, and I leave it running in a fairly stable enviornment.)
I appriceate the insight. Regards Mark Spencer --- On Tue, 8/30/11, Tom Van Baak <[email protected]> wrote: > From: Tom Van Baak <[email protected]> > Subject: Re: [time-nuts] Question for any HP105 owners > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Received: Tuesday, August 30, 2011, 2:25 PM > Mark, > > Let me explain the sqrt(2) thing. > > Since you have a number of oscillators you have probably > already > compared them to each other to see which one is best, or > which > pair is best. > > When you compare the FTS1050 against the HP105 remember > that the ADEV numbers you obtain are always the rms sum of > the instabilities of the DUT, the REF, and the 5370B. At > first you > can't quite know how much of the measured instability at > each > tau is due to each of the three parts. > > So the trick -- if you are comparing two of your best > oscillators > at tau 100 s and get something like 1e-12 you can assume > that > worst-case they are sqrt(2)*1e-12, or 7e-13 each. > > Why? Because your 1e-12 measurement is the rms sum of DUT > and REF and comparator noise. At 100 s the 5370B noise is > down > to, say, 2e-13. The rms of 2e-13 plus 7e-13 plus 7e-13 = > 10e-13, > or 1e-12. > > In other words, when you get a DUT that approaches to how > good > your REF is, your ADEV measurements may *understate* how > good the DUT really is. > > Once you've played with this you can try the next trick > which is the > so-called 3-cornered hat. The goal in the end is to better > determine > the real ADEV (not relative ADEV) of your measurement > system > and each of your oscillators. > > /tvb > > > ----- Original Message ----- > From: "Mark Spencer" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]>; > "Tom Van Baak" <[email protected]> > Sent: Tuesday, August 30, 2011 8:00 AM > Subject: Re: [time-nuts] Question for any HP105 owners > > > Thanks Tom, the reference oscilator is a Datum FTS > 1050. I've used both a HP 5370B and my Tek 2252 scope > as time > interval counter and looked at the data files with Plotter > and Time Lab. The results are all more or less the > same for > ADEV at 100 seconds. > > With regards to the sqrt(2) removal I'm not familiar with > that phrase but the measurements I was making were for ADEV. > > Using Plotter I also removed the small ammount of drift but > the ADEV values didn't change much. > > > My HP105B has the older style (non 10811) > oscilator. It does out perform all the > 10811's that I own (especially with > regards to longer term stability.) > > Regards > Mark Spencer > > > --- On Tue, 8/30/11, Tom Van Baak <[email protected]> > wrote: > > > From: Tom Van Baak <[email protected]> > > Subject: Re: [time-nuts] Question for any HP105 > owners > > To: "Discussion of precise time and frequency > measurement" <[email protected]> > > Received: Tuesday, August 30, 2011, 2:09 AM > > Hi Mark, > > > > What reference oscillator and measurement system did > you > > use? > > Is that with or without a sqrt(2) removed? Is your > HP105 > > the older > > style with the 00105 brick oscillator or a newer one? > > > > The modern HP105 is essentially a well engineered > wrapper > > around > > a 10811 oscillator so the performance you see will be > that > > of the > > 10811. Your 3e-12 measurement beats the spec for a > 10811 > > (1e-11 > > at tau 100 s) by a wide margin. > > > > It is possible that the 10811 used in HP105 met some > higher > > spec > > or were hand selected. I don't know. Perhaps someone > from > > HP > > (Rick?) could clarify this for us. We do know there > are a > > number > > of different grades of 10811. > > > > One lesson you learn if you test many 10811 is that > they > > can vary > > by quite a lot (an order of magnitude or more), even > those > > with the > > same part number in the same instrument model. > > > > For example, see the tau 100 second point of a dozen > > 10811's: > > http://leapsecond.com/pages/z3801a-osc/z3801a-13-adev-m.gif > > Notice they all are under the 1e-11@100s spec, but > some > > are > > much better than others. It's the luck of the draw. > And one > > reason > > why some of us troll eBay for old or cheap 10811 > hoping to > > find > > one that's better than the previous best. > > > > /tvb > > > > ----- Original Message ----- From: "Mark Spencer" > <[email protected]> > > To: <[email protected]> > > Sent: Saturday, August 27, 2011 4:53 PM > > Subject: [time-nuts] Question for any HP105 owners > > > > > > > Just curious what a typical ADEV figure is for > the > > HP105 ? Mine seems to be approx 3X10-12 at 100 > > seconds. Just curious what results any other HP105 > > owners have seen in practice. > > > > > > Thanks in advance > > > Mark VE7AFZ > > > > > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
